Coronary heart disease (CHD) is the leading cause of death in women. Observational studies suggest that postmenopausal estrogen replacement therapy (ERT) reduces the risk of a new CHD event by 50% in healthy women, and by 80% in women with prior CHD. Whether the addition of progestin (PERT) to prevent estrogen-induced endometrial cancer alters the risk of CHD is unknown. A total of 3,252 postmenopausal women with coronary disease are being randomized to one of three blinded regimens: ERT, PERT or placebo.